Hi,
I have a simple circuit (attached) running an L7812CV linear voltage regulator that provides 12V output, 1.5A max output current and is rated at a maximum input voltage of 35V (datasheet attached). It powers a GPS device that can run between 8V and 33V. The point of this circuit is to prevent the GPS device from overheating when in 24V trucks as the device gets quite hot at voltages above 12V and sometimes sustains thermal damage if the truck cab has been sitting in the sun for a prolonged period of time.
I'm currently bench testing the attached design. Something strange happens if I feed the regulator more than 26V. The GPS device still draws its usual current (about 100mA) but then suddenly drops to 40mA as if the device has gone into some kind of sleep mode then reboots itself over and over again. I've checked the voltage and current being fed to the device and it is consistent. All data is shown in the attached image.
When the regulator is fed 26V or less the GPS device works fine, when fed any voltage between 8V and 33V directly from the voltage source without the regulator it works fine. I've checked the voltage drop across the GPS device and the current to the device and it all seems consistent (i.e. all current drawn from the power supply is going to the device and the voltage across it is 11.7V even when it seems to go into sleep/low power mode).
Since it works fine below 26V and works fine without the regulator (ignoring the heat issue), I tried testing another circuit that I've attached below.
With this design, the device does not go into any kind of sleep mode even when Vin >26V. This leads me to assume the problem is caused by the regulator being fed a high voltage compared to its output, however I can't wrap my head around why it is happening despite the consistent voltage and current fed to the device.
If anyone could offer their two cents on why this is happening so I may understand and rectify the problem I would be hugely appreciative. My only other suggestion is that perhaps I've damaged something in the regulator during solder and fitting heat shrink sleeves?
I have a simple circuit (attached) running an L7812CV linear voltage regulator that provides 12V output, 1.5A max output current and is rated at a maximum input voltage of 35V (datasheet attached). It powers a GPS device that can run between 8V and 33V. The point of this circuit is to prevent the GPS device from overheating when in 24V trucks as the device gets quite hot at voltages above 12V and sometimes sustains thermal damage if the truck cab has been sitting in the sun for a prolonged period of time.
I'm currently bench testing the attached design. Something strange happens if I feed the regulator more than 26V. The GPS device still draws its usual current (about 100mA) but then suddenly drops to 40mA as if the device has gone into some kind of sleep mode then reboots itself over and over again. I've checked the voltage and current being fed to the device and it is consistent. All data is shown in the attached image.
When the regulator is fed 26V or less the GPS device works fine, when fed any voltage between 8V and 33V directly from the voltage source without the regulator it works fine. I've checked the voltage drop across the GPS device and the current to the device and it all seems consistent (i.e. all current drawn from the power supply is going to the device and the voltage across it is 11.7V even when it seems to go into sleep/low power mode).
Since it works fine below 26V and works fine without the regulator (ignoring the heat issue), I tried testing another circuit that I've attached below.
With this design, the device does not go into any kind of sleep mode even when Vin >26V. This leads me to assume the problem is caused by the regulator being fed a high voltage compared to its output, however I can't wrap my head around why it is happening despite the consistent voltage and current fed to the device.
If anyone could offer their two cents on why this is happening so I may understand and rectify the problem I would be hugely appreciative. My only other suggestion is that perhaps I've damaged something in the regulator during solder and fitting heat shrink sleeves?
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