Low Ohms Adaptor For DMMs Based On An LM317 Regulator

This adaptor circuit is
essentially a 100mA constant current source. It is applied across a
low-value resistor of unknown value (ie, the resistance to be measured)
and the resulting voltage drop can then be measured by a digital
multimeter (DMM). Setting your DMM
to the 200mV range will enable it to measure up to 2O with high
resolution while the 2V range will give a maximum resistance measurement
of 20O. Construction could consist of mounting the LM317 adjustable
3-terminal regulator inside a small plastic box together with the
battery and two resistors connected to the output and Adj pins.

Low Ohms Adaptor Circuit For DMMs Based On An LM317 Regulator

Low Ohms Adaptor Circuit Diagram For DMMs Based On An LM317 Regulator

No on/off switch is required since no current will be drawn when no
external resistance is connected across the Test terminals. Accuracy
using 1% resistors should be within 5% and this could be improved by
measuring the current, adjusting the resistance between the output and
Adj pins of the LM317 to provide a precise 100mA. Before using the
adaptor, check that your meter is not likely to be damaged by having the
full output (6V+) applied when it is set to a low voltage range.
Similarly, be aware that the voltage and current output of the adaptor
may damage components if you use it for “in-circuit” tests.

Author: Peter Chamberlain – Copyright: Silicon Chip

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Drill Speed Regulator

A mini-drill machine is
always needed in drilling the printed circuit board. It is usually
powered by batteries that limit the drill’s capacity.Using a power
supply adaptor with a speed regulator like the one featured here can
certainly improve the performance of the drill.

The speed regulator can maintain the speed of the drill no matter
what load is encountered by the drill.Potentiometer P2 controls the
speed of the mini-drill. P1 sets the maximum voltage allowed by the
mini-drill.

Drill speed regulator circuit schematic

Drill speed regulator circuit schematic

Caution! Danger of electrocution!
Extreme shock hazard. You are working a line voltage of 220 Volts AC.

Mini drill speed regulator PCB

Mini-drill speed regulator PCB

Mini drill speed regulator PCB

Mini-drill speed regulator PCB

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Low Ohms Adaptor For DMMs Based On An LM317 Regulator

This adaptor circuit is
essentially a 100mA constant current source. It is applied across a
low-value resistor of unknown value (ie, the resistance to be measured)
and the resulting voltage drop can then be measured by a digital
multimeter (DMM). Setting your DMM
to the 200mV range will enable it to measure up to 2O with high
resolution while the 2V range will give a maximum resistance measurement
of 20O. Construction could consist of mounting the LM317 adjustable
3-terminal regulator inside a small plastic box together with the
battery and two resistors connected to the output and Adj pins.

Low Ohms Adaptor Circuit For DMMs Based On An LM317 Regulator

Low Ohms Adaptor Circuit Diagram For DMMs Based On An LM317 Regulator

No on/off switch is required since no current will be drawn when no
external resistance is connected across the Test terminals. Accuracy
using 1% resistors should be within 5% and this could be improved by
measuring the current, adjusting the resistance between the output and
Adj pins of the LM317 to provide a precise 100mA. Before using the
adaptor, check that your meter is not likely to be damaged by having the
full output (6V+) applied when it is set to a low voltage range.
Similarly, be aware that the voltage and current output of the adaptor
may damage components if you use it for “in-circuit” tests.

Author: Peter Chamberlain – Copyright: Silicon Chip

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Supply Voltage Monitor

A circuit for monitoring
supply voltages of ±5 V and ±12 V is readily constructed as shown in
the diagram. It is appreciably simpler than the usual monitors that use
comparators, and AND gates. The circuit is not
intended to indicate the level of the inputs. In normal operation,
transistors T1 and T3 must be seen as current sources. The drop across
resistors R1 and R2 is 6.3 V (12 –5 –0.7). This means that the current
is 6.3mA and this flows through diode D1 when all four voltages are
present. However, if for instance, the –5 V line fails, transistor T3
remains on but the base-emitter junction of T2 is no longer biased, so
that this transistor is cut off. When this happens, there is no current
through D which then goes out.

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Supply Voltage Monitor

A circuit for monitoring
supply voltages of ±5 V and ±12 V is readily constructed as shown in
the diagram. It is appreciably simpler than the usual monitors that use
comparators, and AND gates. The circuit is not
intended to indicate the level of the inputs. In normal operation,
transistors T1 and T3 must be seen as current sources. The drop across
resistors R1 and R2 is 6.3 V (12 –5 –0.7). This means that the current
is 6.3mA and this flows through diode D1 when all four voltages are
present. However, if for instance, the –5 V line fails, transistor T3
remains on but the base-emitter junction of T2 is no longer biased, so
that this transistor is cut off. When this happens, there is no current
through D which then goes out.

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0 to 40V Lab Power Supply

A very lab adjustable
power supply that can provide an output voltage between 0 and 60 volts
can be designed using this circuit diagram . This lab power supply can
be designed with LM723 chip or for higher output voltages, with L146
.Output current is also adjustable, but once established, is always
effective. Table 1 shows the values to be modified to have three
different versions of the maximum output voltage (30, 40 and 60 V).

Electrical diagram below shows the alternative 40 V / 0.8 using L146
chip because it can stabilize higher output voltage, much better than
the LM723. Normally, 2 V is the minimum voltage stabilized that even an
integrated circuit can provide. Resistive network R3, R4 and R5, R6
“kill” this restriction so that output can be set to 0 V with
potentiometer P2.

Depending on the output requirements, will be decided on the type
and the semiconductor capacitors to be used. Output current must be
limited so as to keep power dissipation of 40 W. T3 under maximum output
current for 40 V version is 0.8 A. It can connect two parallel 2N3055
transistors (with emitter resistors) to double the current output, but
in this case requires a 2 A transformer

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0 to 40V Lab Power Supply

A very lab adjustable
power supply that can provide an output voltage between 0 and 60 volts
can be designed using this circuit diagram . This lab power supply can
be designed with LM723 chip or for higher output voltages, with L146
.Output current is also adjustable, but once established, is always
effective. Table 1 shows the values to be modified to have three
different versions of the maximum output voltage (30, 40 and 60 V).

Electrical diagram below shows the alternative 40 V / 0.8 using L146
chip because it can stabilize higher output voltage, much better than
the LM723. Normally, 2 V is the minimum voltage stabilized that even an
integrated circuit can provide. Resistive network R3, R4 and R5, R6
“kill” this restriction so that output can be set to 0 V with
potentiometer P2.

Depending on the output requirements, will be decided on the type
and the semiconductor capacitors to be used. Output current must be
limited so as to keep power dissipation of 40 W. T3 under maximum output
current for 40 V version is 0.8 A. It can connect two parallel 2N3055
transistors (with emitter resistors) to double the current output, but
in this case requires a 2 A transformer

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0V to 50 Volt Variable Regulator

A very simple variable
power supply circuit can be made using this electronic circuit diagram
.This variable regulator circuit will provide an variable regulated
output voltage , between 0 and 50 volts . The CA3140 operational
amplifier compares the regulator output to a reference voltage , that
depends on the R9 value.

0V to 50 Volt Variable Regulator Circuit

0V to 50 Volt Variable Regulator Circuit

The output voltage will be nominally twice the voltage between the
positive input ( noninverting ) of the CA3140 and ground . The
unregulated input voltage must be around 60 volts The output voltage can
be set between 0 an 50 volts using R9 potentiometer .The 2N3055
transistors must be mounted on a heatsink , to prevent the overheating
of transistors .

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Low Power 12V Transformerless Power Supply

Many circuits can be
powered directly from the mains with the aid of a series capacitor (C1).
The disadvantage of this approach is that usually only one half cycle
of the mains wave-form can be used to produce a DC voltage. An obvious
solution is to use a bridge rectifier to perform full-wave
rectification, which increases the amount of current that can be
supplied and allows the filter capacitor to be smaller. The accompanying
circuit in fact does this, but in a clever manner that uses fewer
components. Here we take advantage of the fact that a Zener diode is
also a normal diode that conducts current in the forward direction.
During one half wave, the current flows via D1 through the load and back
via D4, while during the other half wave it flows via D3 and D2. Bear in
mind that with this circuit (and with the bridge rectifier version), the
zero voltage reference of the DC voltage is not directly connected to
the neutral line of the 230-V circuit.

This means that it is usually not possible to use this sort of
supply to drive a triac, which normally needs such a connection.
However, circuits that employ relays can benefit from full-wave
rectification. The value of the supply voltage depends on the
specifications of the Zener diodes that are used, which can be freely
chosen. C2 must be able to handle at least this voltage. The amount of
current that can be delivered depends on the capacitance of C1. With the
given value of 220nF, the current is approximately 15mA. A final
warning: this sort of circuit is directly connected to mains voltage,
which can be lethal. You must never come in contact with this circuit!
It is essential to house this circuit safely in a suitable enclosure.

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0V to 50 Volt Variable Regulator

A very simple variable
power supply circuit can be made using this electronic circuit diagram
.This variable regulator circuit will provide an variable regulated
output voltage , between 0 and 50 volts . The CA3140 operational
amplifier compares the regulator output to a reference voltage , that
depends on the R9 value.

0V to 50 Volt Variable Regulator Circuit

0V to 50 Volt Variable Regulator Circuit

The output voltage will be nominally twice the voltage between the
positive input ( noninverting ) of the CA3140 and ground . The
unregulated input voltage must be around 60 volts The output voltage can
be set between 0 an 50 volts using R9 potentiometer .The 2N3055
transistors must be mounted on a heatsink , to prevent the overheating
of transistors .

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