2 DC power supply protection circuits

The 3-pin regulator 7800 series get very popular. I also like it. Because it is convenient and affordable.

Although inside it has short circuit protection.

But often, it would have been damaged when a short circuit.

So, we should use a good power supply protection circuit.

For instance, I would suggest two circuits. We use a simple technique.

The more secure without having to change the IC-regulator frequently.

1. Electronic Fuse for Regulator

As we know 78xx series voltage regulator can give 1A. But when short circuit them may be damaged.

See in the circuit below.

power supply protection circuit using electronic fuse

We use an electronic fuse circuit to protect 78XX safe. When short-circuit occur. This circuit will stop powering the current and voltage immediately to prevent the loss.

How it works

When entering the input voltage to the circuit. Both transistors Q1 and Q2 are in a bistable multivibrator circuit.

First, Q2 will start. But Q1 stops. Because C1 connected to the base of Q1. It is charging. So, the collector voltage of Q1, to bias the base pin of Q3 through R4. That cause Q3 conducts.

And Q4 will conduct too.

So, there is a voltage input to pin 1 of IC1. It causes the output voltage any load.

However, if there is a short circuit. D1 works like connecting to the ground.

That makes the Q2 base have voltage is about 0.3V. Then, Q2 stop the working of the bistable circuit.

They change the operating to cause Q1 runs. So, Q3, Q4, and 78xx IC stop working. So, no the output voltage.

If you want IC works again. You need to press S1 switch. To reset the circuit to return the working.


Or the bistable multivibrator to work and control Q4 work again too.

Parts lists

Q1-Q3: BC547 NPN transistors
Q4: TIP125 Darlington transistor
D1: BAT85 Diode
IC1: 7800 Regulator series
S1: Pushbutton switch
0.25 Resistors, tolerance 5%
R1, R5: 4.7K
R2, R3: 22K
R4: 100K
R5: 4.7K
R6: 3.3K
C1: 0.1uF 50V Ceramic

2. Fast TTL Power Supply protection using SCR

You may know that TTL requires a constant 5V power supply. Even a little over-voltage. It also can destroy TTL chips very rapidly.

And, it doesn’t happen often. When using the 7805 regulators.

The use of a normal fuse is a good and a save money choice.

The TTL safe from too high. Because voltage is low almost is 0V.
While Fust will blow very fast.

So, IC-78xx series is saved from over-current too.

As it happens, this is the most common type of stabilizer failure, so that the protection is necessary for any TTL circuit of any significance.

Some use CMOS in digital circuits. Because they use wide voltage power supply 3V to 16V.

But most circuits use more TTL inside and still use 5V power supply.

So, the power protection circuit has necessary for the Regulator and others.

Fast TTL Power Supply protection using SCR

How it works

In the circuit above. If the voltage at the output terminals rises above 6.2V. The Zener diode conducts charging capacitor C4.

This voltage will trigger the silicon-controlled rectifier (SCR) turn-on.

It will quickly short circuit output to ground very fast. The supply rails blow the fuse immediately.

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This Post Has One Comment

  1. TIP140 of Logic error in connection.

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