Power supply 5v regulator - what's wrong with this picture? (mr. do)
I'm trying to get my Universal power supply working. Right now the regulated 5v supply is putting out 10v, which is the same voltage as the input to the regulator. So initially I thought the regulator was bad, but I got a new one and the same problem is happening.
Here is the circuit for the 5v supply. The input is 9vac.
There is a 20 watt 3.9 ohm resistor connected between the input and the output. Seems kinda screwy to me, though I'm sure that circuit diagram is correct in that regard. But the effect is that it is pulling up the output to 10v. If I disconnect the resistor, the output is 5.03v. Bear in mind I do not have this connected to my mr do board (I don't want to fry it with 10v!).
I would love an explanation of what that resistor is supposed to do (the datasheet for the 78H05 regulator doesn't have such a resistor in the sample circuit).
Even more so, can anyone tell from this circuit what might be wrong with my PS?
I'm trying to get my Universal power supply working. Right now the regulated 5v supply is putting out 10v, which is the same voltage as the input to the regulator. So initially I thought the regulator was bad, but I got a new one and the same problem is happening.
Here is the circuit for the 5v supply. The input is 9vac.
There is a 20 watt 3.9 ohm resistor connected between the input and the output. Seems kinda screwy to me, though I'm sure that circuit diagram is correct in that regard. But the effect is that it is pulling up the output to 10v. If I disconnect the resistor, the output is 5.03v. Bear in mind I do not have this connected to my mr do board (I don't want to fry it with 10v!).
I would love an explanation of what that resistor is supposed to do (the datasheet for the 78H05 regulator doesn't have such a resistor in the sample circuit).
Even more so, can anyone tell from this circuit what might be wrong with my PS?
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