After doing tests on the DTL150 electronic load, I also purchased an Atorch DL24 unit (£19 delivered to the UK) and repeated a few of the tests.
- MOSFET Vgate (see attached traces)
DS1Z_CC_0A01.png CC Mode, 001A, ON. The Vgs ON threshold is approximately 3.7V.
DS1Z_CC_BTN_OFF1.png CC Mode, 1A, ON to OFF using ON/OFF button. Off time <50ms.
DS1Z_CC_BTN_ON1.png CC Mode, 1A, OFF to ON using ON/OFF button. On time <50ms.
DS1Z_CC_PSU_OFF1.png CC Mode, 1A, ON to OFF when switching off the PSU (see note 1)
DS1Z_CC_PSU_OFF2.png CC Mode, 1A, ON to OFF when switching off the PSU (see note 2)
Notes
1. Prior to fitting the Zener diodes between the MOSFET gate and source.
In this case, when the PSU is initially turned off, the Vgate voltage goes to maximum ~11V until the firmware detects that there is no sense voltage (500ms) and then turns the MOSFET off in <100ms.
2. After fitting back-to-back 6V8 Zener diodes between the MOSFET gate and source.
In this case, when the PSU is initially turned off, the Vgate voltage goes to the clamped voltage of ~7.5V until the firmware detects that there is no sense voltage (500ms) and then turns the MOSFET off in <100ms. As previously noted, the Zener diodes will ensure that Vgs is well within the specified limit of +/-20V, although there is no evidence that this is exceeded without the Zener diodes fitted. Clamping to 7.5V may provide some degree of current limiting.
- CC Setting
Unlike the DTL150, the DL24 worked as expected down to an ISET current of 0.01A.
As previously reported on the DL24, the current and voltage reading do have some variation, but seem perfectly acceptable.
- Serial Interface
The serial interface seems to work more or less as expected, although there are some quirks with the Atorch PC software and some anomalies with the value formats for control data compared to available information on the Internet.
The DL24 automatically sends out a 36-byte frame every second.
The DL24 responds with 7-byte frames to query frames (6-byte) sent from the PC software.
The DL24 parameters can be set with the control frames (6-byte) sent from the PC software.
The PC software allows selection of 36-byte (Protocol 1) or 7-byte (Protocol 2) processing.
Oscilloscope traces for the serial interface are attached.
DS1Z_Serial_36Byte_Auto.png : DL24 to PC, Auto sent 36-byte frame every second.
DS1Z_Serial_36Byte_SOF.png : DL24 to PC, shows the start of the 36-byte frame.
Structure = 0xFF 0x55 0x01 0x02 < Voltage 24 bits > < Current 24 bits >
Voltage = 0x000033 = Dec 51, Voltage (V) = Dec value / 10 = 5.1 V
Current = 0x0003E9 = Dec 1001, Current (A) = Dec value /1000 = 1.001 A
DS1Z_Serial_CTRL_Off.png : PC to DL24, turn load OFF.
Structure = 0xB1 0xB2 CMD D1 D2 0xB6
CMD = 0x01 = Enable/Disable
D1:D2 = 0x0000 = Disable Load
DS1Z_Serial_CTRL_On.png : PC to DL24, turn load ON.
Structure = 0xB1 0xB2 CMD D1 D2 0xB6
CMD = 0x01 = Enable/Disable
D1:D2 = 0x0100 = Enable Load
DS1Z_Serial_CTRL_SetI_1A5.png : PC to DL24, set load current.
Structure = 0xB1 0xB2 CMD D1 D2 0xB6
CMD 0x02 = Set I
D1:D2 = 0x0096 = Dec 150, Current (A) = Dec value / 100 = 1.50 A
Summary
Overall I think that the DL24 is slightly better than the DTL150, but both are excellent for the cost. The DL24 seems to provide CC control down to lower currents and the serial monitoring/control interface could be useful.
I have only tested currents up to around 5A and power of 70W. With the supplied heatsink and fan, both the MOSFET and protection diode seem to be at acceptable temperatures.
Regards, Dave